1. Field of the Invention
The present invention relates to an ignition diagnosis apparatus for diagnosing a failure or an abnormality in the ignition system of an internal combustion engine.
2. Description of the Related Art
In recent years, problems of environmental conservation and fuel depletion have been raised, and also in the automobile industry, solutions to these problems have become big issues. As one of the solutions to the problems, a multi-point ignition method has been drawing attention; in the multi-point ignition method, a plurality of ignition sources is arranged in the combustion chamber of a single cylinder, and an inflammable fuel-air mixture is ignited to combust at a plurality of positions in the combustion chamber so that the thermal efficiency is raised and hence the engine efficiency is maximized.
However, the multi-point ignition method, in which the engine efficiency is raised by igniting an inflammable fuel-air mixture at a plurality of positions in an combustion chamber, has a problem, on the other hand, that a failure in part of the ignition positions makes it impossible to obtain a target engine efficiency; therefore, it is required to diagnose and appropriately deals with the failure in the ignition system.
To date, as an apparatus for diagnosing a failure or an abnormality in the ignition system of an internal combustion engine, there has been known an apparatus (for example, refer to Japanese Patent No. 3507793) in which combustion of an inflammable fuel-air mixture or extinction is detected based on whether or not there is produced an ion current obtained by applying a voltage to ions that are produced when the inflammable fuel-air mixture is combusted.
In a conventional apparatus disclosed in Japanese Patent No. 3507793, in the case of an internal combustion engine utilizing the multi-point ignition method in which a plurality of ignition sources is arranged in the combustion chamber of a single cylinder, it cannot be determined that part of the ignition sources are in a failure state, and in the case where, even though combustion does not occur in all the ignition sources provided at a plurality of positions, combustion occurs at any one of the positions in the cylinder, the combustion produces ions and hence an ion current is detected; therefore, there has been a problem that it is determined that because no extinction has occurred, i.e., ignition or lighting has normally occurred, there exists no failure or abnormality in the ignition system.